Normally, business enterprises stock items of inventory so that the items are immediately available to customers upon demand without the need for ordering them from the business' source when the customer makes his purchase. It is a common occurrence for the number of items in inventory to be reduced by sales to the point at which it would be impossible for the business enterprise to timely reorder inventory to avoid completely running out of stock prior to new stock arriving from its supplier. In particular, stock may be reduced below a critical amount and then reordered only to become completely depleted before the ordered shipment can arrive from the supplier. Likewise, the same problem is present in hospitals and in military operations where the depletion of inventory supplies can have catastrophic results.
The prior art includes various mechanical stock registers that record and display the number of items taken from stock, and display the number of items presently in stock. U.S. Pat. No. 1,539,919 to Swift discloses a stock register for registering quantities of commodities presently in stock, and for counting quantities as taken from stock. U.S. Pat. No. 2,663,495 to Ramsell et al., discloses an electrical apparatus for selectively computing and keeping count of inventory of a number of different items of manufacture as they are produced and disposed of, and also for giving a current record of unfilled orders.
In addition, the prior art discloses many devices for monitoring the number of items or people within a closed or confined area. Specifically U.S. Pat. No. 1,872,782 to Messick, et al. discloses a registering device to tally the number of people in a railroad car; and U.S. Pat. No. 3,978,321 to Doggett discloses a portable handcarried automobile counting device for monitoring the number of cars in a parking lot.
Finally, U.S. Pat. No. 4,500,880 to Gomersall, et al. discloses a computer driven informational display system adapted for use with the standard Universal Product Code to display pricing and other associated information regarding shelf inventory.